Titanium carbo-nitride complex silicon nitride tool

Abstract

Titanium carbo-nitride complex silicon nitride tool is composed mainly of titanium carbo-nitride and silicon nitride and contains 10 to 56 wt % of Ti, 11.6 to 51 wt % of Si and 1 to 21 wt % in total of one or two or more of Ce, Y, Yb and Dy. The tool is mainly composed of Si3N4 superior in both strength and resistance against thermal shock and TiCN superior in the effect of suppressing reactivity of Si3N4 with Fe and exhibiting high hardness. By using oxides CeO2, Y2O3, Yb2O3 and Dy2O3 as sintering aid so that the sum of the amounts of Ce, Y, Yb and Dy will be in the above range, both the resistance against flank notch (wear) of the end edge and resistance against thermal shock are improved resulting in improved durability as compared to the conventional silicon nitride cutting tool.

What is claimed is: 
     
       1. A titanium carbo-nitride complex silicon nitride tool consisting essentially of titanium carbo-nitride and silicon nitride, wherein said tool comprises, based on the total weight of said tool, 10 to 56 wt % of Ti, 11.6 to 51 wt % of Si and 1 to 21 wt % of at least one element selected from the group consisting of Ce, Y, Yb and Dy.   
     
     
       2. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1 wherein one or two or more of Ce, Y, Yb and Dy are contained in an amount of 3 to 15 wt % in total. 
     
     
       3. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1 having a Vickers hardness at room temperature of 16 GPa or higher and a bending strength at 1000° C. of not lower than 800 MPa. 
     
     
       4. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1 containing 19 to 41 wt % of Ti and 21 to 42.8 wt % of Si. 
     
     
       5. The titanium carbo-nitride complex silicon nitride tool as defined in claim 4 having a Vickers hardness at room temperature of 17 GPa or higher and a bending strength at 1000° C. of not lower than 850 MPa. 
     
     
       6. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1 containing 41 to 56 wt % of Ti and 11.8 to 28.8 wt % of Si. 
     
     
       7. The titanium carbo-nitride complex silicon nitride tool as defined in claim 6 having a Vickers hardness at room temperature of 18 GPa or higher. 
     
     
       8. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1, wherein the tool is coated with a coating layer having a film thickness of 1 to 5 μm, said coating layer being mainly composed of a solid solution of one or two or more of carbide, nitride, carbo-nitride and oxide of Al, and carbide, nitride, carbo-nitride and oxide of Ti, provided that the grain size of constituent grains is not more than 0.5 μm. 
     
     
       9. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1, wherein said Ti is present in an amount of at least 21 wt %. 
     
     
       10. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1, wherein said Ti is present in an amount of at least 41 wt %. 
     
     
       11. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1, wherein said Ti and said Si are present in an amount of at least 48.5 wt %. 
     
     
       12. The titanium carbo-nitride complex silicon nitride tool as defined in claim 1, wherein said Ti and said Si are present in an amount of at least 51 wt %. 
     
     
       13. A sintered article of titanium carbo-nitride complex silicon nitride ceramic produced according to the following steps: (1) preparing a starting powder mix comprising 10 to 60 vol % of TiC x  N 1-x  (0.3<x≦0.5), 0.5 to 10 vol % of at least one oxide selected from the group consisting of CeO 2 , Y 2  O 3 , Yb 2  O 3  and Dy 2  O 3 , and the balance being silicon nitride, and   (2) sintering the starting powder mix under application of pressure in an inert or nitrogen containing atmosphere at a temperature of 1500 to 1900° C.   
     
     
       14. A ceramic cutting tool formed of the sintered article as defined in claim 13. 
     
     
       15. The ceramic cutting tool formed of the sintered article as defined in claim 14, which has a coating layer consisting essentially of a solid solution of at least one compound selected from the group consisting of carbides, nitrides, carbo-nitrides and oxides of Al, carbides, nitrides, carbo-nitrides and oxides of Ti, provided that constituent grains of said coating layer have a grain size of not more than 0.5 μm. 
     
     
       16. The ceramic cutting tool formed of the sintered article as defined in claim 15, wherein said coating layer has a thickness of 1 to 5 μm. 
     
     
       17. A titanium carbo-nitride complex silicon nitride tool consisting essentially of titanium carbo-nitride and silicon nitride, wherein said tool comprises, based on the total weight of said tool, 10 to 50 wt % of Ti, 11.6 to 51 wt % of Si and 1 to 21 wt % of at least two elements selected from the group consisting of Ce, Y, Yb and Dy.   
     
     
       18. The titanium carbo-nitride complex silicon nitride tool as defined in claim 17, wherein said at least two elements are each present in an amount of at least 1 wt %. 
     
     
       19. The titanium carbo-nitride complex silicon nitride tool as defined in claim 17, wherein said at least two elements are present in a total amount exceeding 3 wt % and X/(X+Y) is in a range from 0.35 to 0.65, wherein said X is wt % of one element of said at least two elements and said Y is wt % of the other element of said at least two elements. 
     
     
       20. A method for producing titanium carbo-nitride complex silicon nitride ceramic comprising: preparing a starting powder mix comprising 10 to 60 vol % of TiC x  N 1-x  (0.3<x≦0.5), 0.5 to 10 vol % of at least one oxide selected from the group consisting of CeO 2 , Y 2  O 3 , Yb 2  O 3  and Dy 2  O 3 , and the balance being silicon nitride, and   sintering the starting powder mix under application of pressure in an inert or nitrogen containing atmosphere at a temperature of 1500 to 1900° C.   
     
     
       21. The method as defined in claim 20, wherein said sintering is carried out by hot pressing (HP) at a temperature of 1850 to 1900° C. 
     
     
       22. The method as defined in claim 20, wherein said sintering is carried out by hot isostatic pressing (HIP) at a temperature of 1500 to 1700° C. 
     
     
       23. The method as defined in claim 22, wherein said HIP is preceded by preliminary sintering at 1550 to 2000° C. in a nitrogen atmosphere. 
     
     
       24. The method as defined in claim 22, wherein said HIP is carried out in an inert gas under a pressure of at least 90 MPa. 
     
     
       25. The method as defined in claim 20, which further comprises a step of further processing the sintered ceramic into a cutting tool.